The picture in “From the Archive”
(“Self-experimenter didn’t suffer,”
SN: 1/28/12, p. 32) shows heavy water
ice sinking in a glass of water while
alongside, light water ice floats. What is
not clear is what kind of water is in the
glasses. If heavy water ice were in a glass
of heavy water, would it also float?
Robert Chester, Tumwater, Wash.

The picture shows a heavy water ice
cube sinking in normal water. Like normal water, heavy water expands when it
freezes, becoming less dense. An ice cube
made of heavy water will thus float in
heavy water. Christoph Salzmann of
University College London offers an illustrative experiment: Fill a glass halfway
with heavy water and halfway with normal water. Then drop in a heavy water ice
cube. The cube will sink until it reaches
the dividing line between the normal and
heavy waters, at which point it will float
midglass. — Elizabeth Quill

Studies of light are ancient
The survey of advances in reflective
light and camera innovations (“The digital camera revolution,” SN: 1/28/12,
p. 22) recalls the 1964 book Byzantine
Aesthetics by Gervase Mathew. The
subject matter of religious symbols was
important, but so was the technique
of setting the colorful tiles. It might be
good to take another look at Byzantine
art and the Neoplatonism of Plotinus
(who died about A.D. 270) and the bridge
between Plato’s shadows and the coming
theories of light, especially sunlight.
Cynthia Shepard, Foster City, Calif.

Aura experiences varyI have never experienced a migraineheadache (“Head agony,” SN: 1/28/12,p. 26) but regularly experience auraslike those in the story. The auras comewith stress and are quite beautiful, look-ing much like the opening scene fromthe old television show Bonanza wherethe flame starts at one point and thenspreads outward on the map. No doubtin times past, people may have thoughtthey were being visited by an angel orhaving a supernatural experience.Joe Kostka, Natrona Heights, Pa.

Memory falters under pressure
The inability to recall what happened
during a feat that requires great concentration doesn’t apply only to athletes
(“Brainy ballplayers,” SN: 1/14/12, p. 22).
As a U.S. Foreign Service officer in the
1980s, I served as notetaker during high-pressure, high-level meetings between
the United States and Soviet Union.
Right after meetings, anxious colleagues
would ask what happened. “I don’t
know,” I would reply. “I’ll have to read
my notes.” My thanks to Science News
for explaining why that happened.
Bruce G. Burton, Fairfax Station, Va.